The pedestrian-crossing marking in Japan is such that rectangular painted portions and non-painted portions are alternately repeated at equal widths and the painted portions and the non-painted portions are equal in width and the width is predefined at 45 cm to 50 cm. On the other hand, for the pedestrian-crossing markings in foreign countries, some markings are such that rectangular painted portions and non-painted portions are different in width, but many markings are such that the sum of the widths of the painted portion and the non-painted portion is constant and the painted portions and the non-painted portions are alternately repeated.
A conventional pedestrian-crossing marking detecting device is directed for extracting an image intensity edge which largely changes in image intensity from image data captured by a camera by use of the fact that pixels of painted portions and pixels of non-painted portions are largely different in an image intensity. Thereby, some conventional pedestrian-crossing marking detecting devices are to calculate an interval between and the number of neighboring image intensity edges and thereby to decide whether the image is a pedestrian-crossing (see Patent Literature 1). The conventional technique will be described below.
FIG. 1 is a block diagram of conventional pedestrian-crossing marking detecting device 1500 described in Patent Literature 1. In FIG. 1, stereo image data obtaining section 1501 uses a stereo camera comprising two imaging systems to obtain a pair of items of image data in which the front of a vehicle including a road surface is simultaneously captured. The image data captured in one imaging system in the pair of items of image data is assumed as target image data, and the image data captured in the other imaging system is assumed as reference image data.
Distance data calculating section 1502 stereo-matches the target image data with the reference image data thereby to calculate a distance in a real space from the stereo camera at each point within the image.
Pedestrian-crossing marking detecting section 1503 detects the existence of a pedestrian-crossing marking in the obtained target image data, and when a pedestrian-crossing marking is present on the image data, pedestrian-crossing marking detecting section 1503 detects the position thereof.
Pedestrian-crossing marking detecting section 1503 includes intensity edge detecting section 1504, width deciding section 1505, interval deciding section 1506 and repetition deciding section 1507.
Intensity edge detecting section 1504 assumes an arbitrary area in the target image data as a calculation range, and detects a intensity edge position in the calculation range. The detection of the intensity edge position within an arbitrary calculation range is performed on the entire range of the target image data. Specifically, the intensity edge position is detected by a typical image processing such as sobel filter.
Width deciding section 1505 extracts an image intensity edge changing from high intensity to low intensity as a start point from the intensity edge positions detected by intensity edge detecting section 1504, and extracts an image intensity edge changing from low intensity to high intensity as an end point therefrom. Then, width deciding section 1505 extracts, from a group of combinations of start point and end point, a combination of start point and end point for which an interval therebetween is the same as or close to a predefined width of a painted portion of the pedestrian-crossing.
Interval deciding section 1506 calculates, from a group of combinations of start point and end point extracted by width deciding section 1505, an interval between the end point in the first combination and the start point in the second combination which is positioned on the same horizontal axis as the end point in the first combination in the target image and is different from the start point in the first combination. Interval deciding section 1506 extracts the first combination in which the interval is the same as or close to a predefined width of a non-painted portion of the pedestrian-crossing.
Repetition deciding section 1507 calculates the number of repetitions of the combination of start point and end point extracted by interval deciding section 1506 in the calculation range, and when the result is the predetermined number of times or more, repetition deciding section 1507 assumes the area as a pedestrian-crossing area.